A multilayer resist process is used for manufacturing integrated circuit elements in order to obtain a higher degree of integration. The multilayer resist process can achieve micro-fabrication. In this process, a composition for forming a lower layer in the form of a liquid is first applied to a substrate and cured to obtain a resist lower layer film. Then, a liquid photo resist composition is applied to the resist lower layer film. Next, a photoresist pattern is obtained by transferring a mask pattern and is developed with an appropriate developer using a reduced projection exposure system (stepper). The pattern is transferred to a resist lower layer film by dry etching. The resist lower layer pattern is finally transferred to a substrate by dry etching. A substrate with a desired pattern can be obtained in this manner. A multilayer process may be called a two-layer resist process if one resist lower layer film is used, and a three-layer resist process if two resist lower layer films are used.
Generally, the resist lower layer film functions as an antireflection film which absorbs radiation reflected by a substrate, and it is common to use a material having a large carbon content. A resist lower layer film with a large carbon content can improve etching selectivity during substrate processing, ensuring a more exact pattern transfer. A thermosetting phenol novolak resin is a well known resist lower layer film. A composition containing a polymer having an acenaphthylene skeleton is also known as a resist lower layer film exhibiting good characteristics (for example, refer to Patent Documents 1 and 2).
Patent Document 1: JP-A-2000-143937
Patent Document 2: JP-A-2001-40293